This giant Buddha statue, which is a national treasure in Japan, is made of bronze. Bronze consists mainly of copper but also contains some tin. Bronze is an example of a solution. A solution is a type of mixture that has the same composition throughout.

How a Solution Forms

A solution forms when one substance is dissolved by another. The substance that dissolves is called the
solute
. The substance that dissolves it is called the
solvent
. The solute is present in a lesser amount that the solvent. When the solute dissolves, it separates into individual particles, which spread throughout the solvent.

Q:
In bronze, what are the solute and solvent?

A:
Because bronze consists mainly of copper, copper is the solvent and tin is the solute. The two metals are combined in a hot, molten state, but they form a solid solution at room temperature.

What’s Your State?

In the example of bronze, a solid (tin) is dissolved in another solid (copper). However, matter in any state can be the solute or solvent in a solution. For example, in a saltwater solution, a solid (salt) is dissolved in a liquid (water). The
Table
below
describes examples of solutions consisting of solutes and solvents in various states of matter. Yon learn more about solutions such as these at this URL:
http://www.youtube.com/watch?v=NsdBUWnG2cQ

Type of Solution: Example

Solute

Solvent

Gas dissolved in gas
: dry air

oxygen

nitrogen

Gas dissolved in liquid
: carbonated water

carbon dioxide

water

Liquid dissolved in gas
: moist air

water

air

Liquid dissolved in liquid
: vinegar

acetic acid

water

Solid dissolved in liquid
: sweet tea

sugar

tea

Water as a Solvent

Salt isn’t the only solute that dissolves in water. In fact, so many things dissolve in water that water is sometimes called the universal solvent. Water is such a good solvent because it is a very polar compound. A polar compound has positively and negatively charged ends. Solutes that are also charged are attracted to the oppositely charged ends of water molecules. This allows the water molecules to pull the solute particles apart.

On the other hand, there are some substances that don’t dissolve in water. Did you ever try to clean a paintbrush with water after painting with an oil-based paint? It doesn’t work. Oil-based paint is nonpolar, so its particles aren’t charged. As a result, oil-based paint doesn’t dissolve in water. (You can see how to dissolve oil-based paint in the
Figure
below
.)

To dissolve a nonpolar solute such as oil-based paint, a nonpolar solvent such as paint thinner must be used.

Like Dissolves Like

These examples illustrate a general rule about solutes and solvents: like dissolves like. In other words, polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. You can see a student’s video demonstrating solutes that do and solutes that don’t dissolve in water at this URL:
http://www.youtube.com/watch?v=ek6CVVJk4OQ&feature=related

Ionic and Covalent Solutes

All solutes separate into individual particles when they dissolve, but the particles are different for ionic and covalent compounds. Ionic solutes separate into individual ions. Covalent solutes separate into individual molecules.

The sugar glucose is a covalent compound. When sugar dissolves in water, it forms individual glucose molecules (C
6
H
12
O
6
). You can see how this happens in the
Figure
below
. Sugar is polar like water, so sugar molecules also have positive and negative ends. Forces of attraction between oppositely charged ends of water and sugar molecules pull individual sugar molecules away from the sugar crystal. Little by little, the sugar molecules are separated from the crystal and surrounded by water. You can watch this happening in the video at the following URL:
http://www.youtube.com/watch?v=hydUVGUbyvU

Summary

A solution forms when one substance dissolves in another. The substance that dissolves is called the solute. The substance that dissolves it is called the solvent.

Solutes and solvents may be any state of matter.

Many solutes dissolve in water because water is a very polar compound.